A fork of Rural Dictionary
It simply means "let me know." Or get back to me with answer. If it already formally exists, I don't know, but I started using it in my e-mails in the '90s for convenience. Today, someone responded "OH!!!!!!" after I replied to his "what's the meaning of that" e-mail. So, there you have it.
In e-mail commonly, consider for example: 1) If you need anything, LMK. 2) What're you guys doing tonight? LMK.
The letters LMK itself stands for 'let me know'. If you are talking about the app 'LMK' then it basically an app where you can meet new people, but it also has a bit of tinder in it as well. People generally don't even use the app as a dating app; they just explore topics such as politics, race, LGBTQ and religion most of the time.
2 lovebirds messaging on LMK "Add me on snapchat, baby cakes "OK, LMK if you added me. Hehehhe get the pun?
lmk means let me know. It is also an app mainly used for Snap Chat. People will say this when they want you to tell them something.
Person 1: okay just lmk when you find out the news Person 2: yeah you'll be the first to know
LMK what you think about us getting married with all this massive dreams coming true for you my dear